1. Field of the Invention
This invention relates to a camera which includes a power supply apparatus for applying, for example, different output voltages separately to a plurality of electrodes and a variable shape mirror with a reflecting surface whose shape varies with the output voltages applied to the electrodes. More particularly, this invention relates to a power supply apparatus and an actuator control apparatus which make the circuit size smaller and realize a good controllability.
2. Description of the Related Art
In recent years, so-called electronic cameras have been popularized. In electronic cameras, an image pickup optical system forms a subject image on a semiconductor imaging element, such as a CCD two-dimensional image sensor, thereby converting the image into an electric signal. The image data about the subject image thus obtained is recorded into a recording medium, such as a semiconductor memory or a magnetic disk.
Electronic cameras of this type have a lens for forming the subject image on the semiconductor imaging element. Most of them use a glass lens whose refractive index and shape are less liable to change due to a change in the temperature or humidity. In recent years, there have been strong demands for lighter weight and lower cost. For this reason, use of plastic lenses in place of glass lenses has been examined. However, since the image formation characteristic of the plastic lens is liable to deteriorate due to a change in the temperature and humidity, use of the plastic lens requires any suitable measure to be taken against changes in the temperature and humidity.
With this backdrop, the applicant of this application has proposed a variable shape mirror element which has an optical reflecting surface and is capable of electrically controlling the shape of the reflecting surface by electrostatic force as written in, for example, Japanese Patent Application No. 11-72557 (Jpn. Pat. Appln. KOKAI Publication 2000-267010). Use of the variable shape mirror element enables a change in the optical characteristic of the plastic lens due to a change in the temperature and humidity to be compensated for by changing the shape of its reflecting surface. Therefore, it is possible to meet the demands for lighter weight and lower cost.
To control the shape of the reflecting surface of the variable shape mirror, that is, to perform control so as to obtain a shape that presents the desired optical characteristic, it is necessary to apply various voltages to a plurality of electrodes the variable shape mirror has. To make the amount of displacement larger, several tens of volts have to be applied.
With the recent trend toward making portable apparatuses smaller, many attempts have been made to cause the apparatus to operate properly for a long time from a small-capacity battery capable of generating only a low voltage. One technique for operating the apparatus on a low voltage for a long time was to use a DC/DC converter.
On the other hand, to make the apparatus smaller, it is necessary to reduce the number of parts. The applicant of this application has constructed a DC/DC converter that provides on/off control of one of the ports of a microcontroller for controlling the entire apparatus without using a special oscillator and uses inductor.
In recent years, microcontrollers have been made smaller in chip size as a result of advances in microfabrication technology. They have also been manufactured at lower cost. The limitation of voltage resistance due to microfabrication is becoming an important control item. Specifically, to use the latest, small, low-cost device, it is essential to invent a device to prevent the power supply voltage from rising above a specific voltage.
On the other hand, it goes without saying that it is necessary to invent a device to control the DC/DC converter more accurately according to the situation and suppress the power consumption to lengthen the service life of the battery, thereby increasing the user's satisfaction level.